As a result of the strict enforcement of controls on harmful emissions from the internal combustion engines of vehicles, particularly of automobiles, a catalytic converter has been adopted as one method of reducing these emissions by converting them into less noxious substance due to their reaction when brought into contact with a catalyst. Various types of catalytic converters are available, such as the downflow type and radial type, but the basic principle lies in placing a catalyst in a casing and purifying the exhaust gas by passing it through the catalyst. The vessel to hold this converter has to be heat-resistant and endurable. The inner casing where the exhaust gas is separated from the catalyst is supposed to be the most vulnerable part of the catalytic converter vessel, because it is exposed to exhaust gas at a temperature as high as about 1000° C., as well as to the weight of the catalyst particles and the exhaust gas pressure. To resist the heat and maintain rigidity under high temperature, it is fabricated of a metal plate which is strong enough to withstand high temperature.

Meanwhile the inner casing is bored with numerous holes so tiny as to prevent the catalyst particles from dropping out of the converter and prevent an increase in the exhaust resistance. Since the catalyst particles are usually in the range of 3-4 mm for reasons of productivity, effective area and activity, the tiny holes in the inner casing have to be less than 2.5 mm when measured in the direction of their minor axis. Thus the inner casing is the least productive part in the catalytic converter vessel.

The tiny holes formed in the inner casing are usually punched holes (round or oval) or louver holes on account of the relationship between diameter and plate thickness. In the case of punched holes, the diameter is so small that the punch and die are often broken and many manhours are required to maintain the tools in good condition. In the case of louver holes, the tools can last a long time but the root of a notch in the louver holes is likely to crack under thermal stress repeatedly acting on the inner casing.

The louver holes are formed by shearing without producing any chips from the plate. As illustrated in the oblique view of FIG. 1, only the cut opening is visible from the front, but from the side holes are visible. In said louver holes, stress concentration is likely to develop at the four corners of the sheared part and therefore, when a heavy thermal stress acts repeatedly, a crack is likely to develop from said four corners toward the area between the holes. Thus the durability of a plate formed with louver holes depends on the area between these holes; the wider said area, the less likely to develop a crack and the higher the rigidity; but the exhaust resistance rises.

The present invention relates to a catalytic converter vessel for exhaust gas purification, which is characterized by increased productivity and durability.

FIG. 1 is an oblique view of a louver hole.

FIG. 2 is a longitudinal sectional view of a catalytic converter vessel according to the present invention.

FIG. 3 is a sectional view taken along the line A-A' of FIG. 2.

The present invention will be explained by referring to the drawings. As illustrated in FIG. 2, which is a longitudinal sectional view of the catalytic converter vessel according to the present invention, and in FIG. 3 which is a sectional view taken along the line A-A' of FIG. 2, the catalytic converter vessel according to the present invention consists of outer casings 1, 1', inner casing 2 and center stay bolt 3. The inner casing 2 having louver holes 4 or punched holes 5 is assembled with plates 6 having punched holes 5 or louver holes 4 opposite the louver holes 4 or punched holes 5 of said inner casing 2 so that these holes are concentrically aligned.

In FIGS. 2 and 3 is illustrated an assembly comprising inner casing 2 with louver holes 4 laid over plate 6 which has punched holes 5 concentrically aligned with said louver holes 4. It is possible to lay plate 6 with concentric louver holes 4 over the inner casing 2 with punch holes 5. Thus in the present invention, when inner casing 2 is bored with louver holes 4, plate 6 with punched holes 5 is laid under said inner case 2; and when inner casing 2 has punched holes 5, plate 6 with louver holes 4 is laid over said inner case 2, so that the two holes are concentrically aligned. Louver holes and punched holes are provided athwart the exhaust gas flow. In these figures, 7 denotes an exhaust gas inlet; 8 denotes an exhaust gas outlet; 9 denotes a catalyst layer; 10 denotes a catalyst bed; and the arrow indicates the travel direction of the exhaust gas.

According to the present invention, the inner casing 2 and plate 6 are assembled one over the other or under the other so that louver holes 4 come over punched holes 5 in coaxial alignment; and then said inner casing and said plate are spot-welded or arc-welded together. When, however, plate 6 is too small, it may be clampled by means of a center stay bolt 3.

When the thermal expansion of plate 6 is too large in view of the difference in temperature, an L-shaped blanket may be attached in such a way that the inner casing 2 and plate 6 can slide along each other.

In the present invention in which punched holes 5 are located inside of louver holes 4, the punched holes 5 can be made larger in diameter than similar punched holes in conventional inner casings because catalyst particles, even if said punch hole diameter is larger than the minor axis and smaller than the major axis of louver holes 4, can be prevented by the projecting part of louver holes 4 from dropping out. In the present invention, since as described above punched holes 5 are larger in diameter than the minor axis and smaller than the major axis of louver holes 4, the four corners of louver holes 4 can be covered by punched holes 5. In this condition the thermal stress applied to said four corners of louver holes 4 is mitigated and thus cracking is less likely to occur at said four corners and the device can have a long life.

In the catalytic converter vessel according to the present invention, the exhaust gas is conveyed from exhaust gas inlet 7 to catalyst layer 9 of the catalyst bed 10, where said gas is purified; and purified gas goes to the exhaust gas outlet 8. The gas comes into contact with the catalyst as it passes through the punched holes 5 and louver holes 4 of plate 6 and inner casing 2 and, moving through those holes in the direction indicated by the arrow, it goes to exhaust gas outlet 8.

Thus, according to the present invention, in which a plate with punched holes or louver holes is assembled together with an inner casing with louver holes or punched holes, the rigidity of the inner casing is increased and the deformation of the inner case due to the weight of catalyst particles, the exhaust gas pressure and vibration can be prevented, thereby vastly improving the durability of the inner case.

At the same time the louver holes formed in the inner case or in the plate are internally protected by concentric punched holes. In consequence, cracking at the corners of the louver holes can be prevented and accordingly the dropping of catalyst particles out of the catalytic converter can be averted.

Since the punched holes 5 are concentrically aligned with the louver holes, the projecting part of the louver hole is mainly effective for the prevention of catalyst particles from dropping out and therefore the diameter of the punched holes may be made larger than that of a catalyst particle. Thus the frequency with which the punch and die used for boring said punch holes are broken can be reduced and the productivity when manufacturing the inner casing or the plate with punch holes can be remarkably increased.